An eye without astigmatism will focus the image at one point on the Retina.

An eye with astigmatism will focus the images at multiple points on the Retina.

In order for the eye to work properly, light coming into the eye must be properly focused on the retina (or the back of the eye). When the image is not focused, there is an irregularity in the eye. This irregularity can be the overall shape of the eye or the curvature of the cornea (the clear outer covering of the eye), or both. The cornea should be curved equally in all directions. Astigmatism occurs when the cornea is curved more in one direction than another.

Astigmatism is quite common and, in the vast majority of cases, it is due simply to variations between people. Just as different people have different shaped feet or hands, people also have different shaped corneas. Rarely astigmatism is caused by chronic lid swellings, benign growth or lesions, and corneal scars, or by keratoconus (a rare condition in which the cornea becomes misshapen and pointed rather than smooth and rounded).

Astigmatism may cause blurred vision, eye strain or even headaches. It can also cause images to appear doubled, particularly at night. Small amounts of astigmatism can be ignored. But if any of its symptoms are present, astigmatism can be corrected by glasses or contact lenses. In most patients soft contact lenses do a good job of correcting for astigmatism, but occasionally, rigid gas permeable contact lens are needed.

Surgery can also be use to help people correct their astigmatism. Surgical correction of astigmatism is done by creating one or more surgical incisions in the cornea or as part of laser vision correction. These procedures help eliminate the uneven curvature and "round out" the cornea. A rounder cornea means objects no longer appear blurred or distorted. Astigmatism correction is sometimes performed at the time of cataract surgery, to reduce or eliminate the patient's need for glasses after surgery.